The problem with iron nitride is, and always has been, low coercivity. Niron hopes that GM can help them figure out a way to design a traction motor that has high performance even with low coercivity magnets. The fact that there are no such motors using iron-nitride magnets suggests that those efforts haven't succeeded yet. https://spectrum.ieee.org/permanent-magnet-motor
If you read the article you'll probably notice that it explicitly states that it is about motors for electric vehicles. These do actually have rare earth metals in them.
Of all the theories being thrown around to explain why this happened, the most plausible, arguably, is the wonkiest. And therefore getting less attention. "Since 1999, Texas has had a deregulated, energy-only market structure, which means that suppliers get paid only for the electricity they produce and sell, and the market is not regulated by the Federal Energy Regulatory Commission. "
I was the editor of that story at Spectrum. Your notes might be very valuable to future writers on that seminal project. If you ever wish to talk about them I can be reached at g dot zorpette at ieee dot org. Thanks for taking the time to share your recollections here.